1. Field of the Invention
The present invention relates to temperature control switches and, more particularly, to one which switches on and switches off promptly, subject to a predetermined temperature.
2. Description of the Prior Art
Temperature control switches are usually used in the load circuit of high power heating appliances (for instance: electric oven), which helps to keep the temperature at the predetermined set point, where the predetermined temperature is adjustable. Conventional temperature control switches usually comprise a casing, where the housing contains two control terminals which feature switching function, and the first control terminal joins a thermostatic bimetal strip that tends to deform due to temperature changes. The thermostatic bimetal strip is provided with a contact that joins the second control terminal; an electric heating device (relatively low power), having its one end connected to the power supply, while the other end to the thermostatic bimetal strip; the casing contains a cam for the regulation of the rotation, where the cam jostles against the bottom part of the thermostatic bimetal strip. Through rotating the cam, the regulation over the magnitude of being uplifted of the thermostatic bimetal strip is then available.
As a voltage is applied across the control terminals, the load circuit of the controlled heating appliance is being activated; meanwhile, the electric heating device located in the temperature control switch is conducted to heat, enabling an uplifted deformation of the thermostatic bimetal strip, subject to a temperature change, which makes the contact on the thermostatic bimetal strip apart from the second control terminal, enabling the electric heating device to be disconnected from the electricity supply and quitted to heat. The thermostatic bimetal strip begins to cool and rebounds off the uplifting, until the contact on the thermostatic bimetal strip joins the second control terminal again, which reactivates the electric heating device to heat. By controlling the cyclic behavior of switching on and off the electric power for the electric heating device of the temperature control switch, to realize the function of controlling the working environment for the high power heating appliance within the predetermined temperature. As the cam is activated to rotate, the predetermined temperature can be altered by changing the magnitude of the uplifting of the thermostatic bimetal strip; therefore, a new temperature is arrived by heating the thermostatic bimetal strip, and at this moment the magnitude of deformation is thus enough to make the strip to depart from the second control terminal which results in an electric disconnection.
However, the problems with the prior art temperature control switches lie in the slowness and smoothness of switch-on and switch-off for the electric power between the contact on the thermostatic bimetal strip and the second control terminal, which is substantially easy to bring forth sparks and high heat, resulting an easy destruction of the contact by fire.